1. Field of the Invention
The present invention relates to throttle bodies that define intake air channels for supplying intake air into engines and that control the flow of the intake air through the intake air channels. The present invention also relates to methods of manufacturing such throttle bodies.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2002-256898 (in particular the fourth embodiment shown in FIGS. 5 and 6) teaches a throttle body that is also called “an intake air control device.” The throttle body has a main body and a valve member. The valve member is rotatably mounted within the throttle body in order to open and close an intake air channel defined within the main body. The valve member is made of resin and is molded via an insertion molding process. More specifically, the main body is first inserted into a mold and the valve member is then resin molded within the main body.
In this publication, it is disclosed that the valve member may have a configuration conforming to the configuration of the inner wall of the main body even after the valve member has contracted after the molding process. The reason for this is that during molding the outer peripheral surface of the molded valve member may contact with the inner wall of the main body. As a result, the configuration of the peripheral surface of the molded valve member conforms to the configuration of the inner wall of the main body. However, because the inner wall of the main body has a simple cylindrical configuration, the following problems may occur when the valve member has contracted during the cooling period after molding. The outer surface at the free peripheral edges of the valve member may not adequately contact with the inner wall of the main body when the valve member has contracted. In some cases, the contraction of the valve member produces clearances between the free peripheral edges and the inner wall of the main body. This may result in causing a leakage of intake air when the valve member is in a closed position, which in turn lowers the mileage of fuel during an idle engine operation.